Release the mapped memory at the end of PrepareHugePages()#7
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March 2, 2026 13:50
Key changes: - Refactor ShmemResizeStructInSegment() to verify internally: Instead of returning the shared memory location pointer for the caller to verify, the function now validates pointer consistency internally via a new helper VerifyAfterShmemUpdateInSegment(), which fatals on mismatch. - Align buffer block pointer before verification in ShmemResizeStructInSegment(): When the target segment is BUFFERS_SHMEM_SEGMENT, align the stored shared memory location pointer to PG_IO_ALIGN_SIZE (via TYPEALIGN) before passing it to the verification helper, matching the alignment applied during initial allocation. - Unify round_off_mapping_sizes() and round_off_mapping_sizes_for_hugepages() into a single round_off_mapping_sizes(): The merged function takes a pagesize parameter (rounds up both shmem_req_size and shmem_reserved to multiples of pagesize, no-op when pagesize is 0). After this change, round_off_mapping_sizes() is only invoked by BufferManagerShmemSize() (for non-main segments) and CalculateShmemSize() (for the main segment). - Refine BufferManagerShmemSize(): Introduce a padsize (header + spinlock aligned to PG_IO_ALIGN_SIZE) as the base offset for each segment's size calculation. For every segment except MAIN_SHMEM_SEGMENT, compute both shmem_req_size and shmem_reserved, then round off to both BLCKSZ and huge page size via round_off_mapping_sizes(). After this change, BufferManagerShmemSize() is only called from CalculateShmemSize() — the previous direct call in pg_resize_shared_buffers() is replaced with a CalculateShmemSize() call. - Refine CalculateShmemSize(): Round off MAIN_SHMEM_SEGMENT sizes to both BLCKSZ and huge page size via round_off_mapping_sizes(). - Parameterize PrepareHugePages(): Remove its internal CalculateShmemSize() call and local mapping_sizes array. The caller now passes pre-computed sizes. - Extract a new method UpdateShmemGUCs(Size size_b): It updates all internal configurations related with Shared Memory. This allows pg_resize_shared_buffers() to call it after a live shared memory resize. - Downgrade ftruncate failure in AnonymousShmemResize(): Change from ereport(ERROR) to elog(WARNING) + return false, making the failure non-fatal so the caller can handle it gracefully.
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